Adaptable Network Service Access through Dynamic Request Routing

ABSTRACT

In an Internet Protocol Multimedia Subsystem (IMS) network in which multiple subscriber data servers are deployed with partitioned subscription data for users, a subscriber location function (SLF) is used to proxy queries to a subscriber data server (such as an HSS) in which subscription data for a user can be found. The SLF receives a query for the subscriber data server, looks up the address of appropriate subscriber data server and proxies the query to the appropriate subscriber data server. Preferably, the SLF is co-located with a subscriber data server.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/687,358, filed Mar. 16, 2007, which claims priority to U.S.Provisional Application Ser. No. 60/783,774, filed Mar. 17, 2006, theentirety of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to methods of, systems for, computerprograms for and apparatus for routing subscriber data queries in acommunications network using the Internet Protocol (IP) MultimediaSubsystem (IMS). More particularly, the present invention relates tomethods of, systems for, computer programs for and apparatus for routingsubscriber data queries in a communications network using the IMS inwhich a subscriber data (for example subscriber data stored in a HomeSubscriber Server (HSS)) is partitioned over several differentsubscriber data servers or functions.

BACKGROUND OF THE INVENTION

The IMS is an architecture for enabling the provision of IP basedmultimedia services in 3G and subsequent mobile and convergedfixed/mobile communications networks. Features of IMS are beingstandardized under the 3rd Generation Partnership Programme (3GPP) and3GPP2. Various network elements in the IMS architecture will now bedescribed by way of background information.

The Home Subscriber Server (HSS) is a database that stores subscriberdata, performs authentication and authorization of subscribers, and canprovide the location of a subscriber user terminal to enable mobility.In the description of IMS used by Verizon Wireless™ the HSS is called aSubscriber Data Manager (SDM) and the terms HSS and SDM are usedinterchangeably in this document.

Call Session Control Functions (CSCFs) are used to manage theestablishment and disestablishment of calls or sessions in the networkin accordance with the instructions of subscribers and ASs using theSession Initiation Protocol (SIP). In the home network of a subscriber,a network element called the Serving CSCFs (S-CSCF) provides the calland session handling functions for the subscriber. The S-CSCF does notmaintain subscriber data locally but queries the HSS for such data usingthe Cx interface based on the DIAMETER protocol. The interrogating-CSCF(I-CSCF) is the contact point within an operator's network for allconnections destined to a subscriber of that network operator, or for aroaming subscriber currently located within that network operator'sservice area. The Proxy CSCF (P-CSCF) is often the entry into thesignaling network, The P-CSCF helps setup and manage sessions, and itforwards messages between IMS networks. It is the first point of contactfor a client accessing the IMS network, whether that client is in itshome network or roaming in a visited network.

Application Servers (ASs) are used to manage the provision of advancedservices to subscribers. ASs may be provided by the network operator andresident in a home network of a subscriber or they may be provided bythird parties and in a foreign network. ASs execute applications whichprovide the control logic for the provision of advanced services such asmessaging, conference calling, voice mail, presence services, locationbased services and so on. Other elements such as media servers may beused to provide some of the required services themselves. ASs may alsoneed to query the HSS for subscriber data and use the Sh interface(which is also based on DIAMETER) to do so.

In the description of IMS used by Verizon Wireless™, there are variousnetwork elements known as the Application Manager (AM), Bearer Manager(BM) and Security manager (SM) each of which may query the SDM forsubscriber data as well as non-IMS applications. In general, the AMscorrespond in 3GPP and 3GPP2 terminology to both CSCFs and ASs.

In some networks, particularly networks with many subscribers orgeographically wide spread networks, multiple HSSs are implemented atdifferent physical sites. This can improve capacity, reduce latency andprovide redundancy. In one approach (replication), identical subscriberdata is stored at all HSS sites and any HSS can service a request inrespect of any subscriber. A typical requirement is for dual or triplesite deployment. A network element can interact with any site buttypically uses nearest for lower latency. In another approach(partitioning), each HSS site is responsible for a subset of the entiresubscriber data for the network. Redundancy may still be employed, butdeployment is partition specific. A network element must query an HSSsite (partition) responsible for the associated subscriber. Accordingly,a routing function is needed to map the subscriber data requests ofnetwork elements to the correct FISS. In 3GPP and 3GPP2 IMS, thisrouting function is called the Subscriber Location Function (SLF). TheSLF and HSS communicate using the DIAMETER protocol.

FIG. 1 shows an exemplary implementation of a partitioned SDM (ie HSS)in a large communications network. The network is divided into a number(in this case 5) geographic regions 10 (only two shown) each having anSDM 14—ie SDMs A, B, C, D and E—forming a partitioned SDM service 12.Each SDM acts as home SDM for subscriber's resident in it's geographicregion. Multimedia and data (MMD) services are provided by AM, BM andother functional elements in each geographic region's cluster 16. Asubscriber will always register with their home SDM. The assumption isthat vast bulk of subscriber activity will be in home region and sointeraction will be with home region elements (AM, BM etc). However,network elements in any region will need to access the subscriber's SDMto terminate sessions to that subscriber and also to support subscriberregistration due to roaming between regions, for example. Elements willneed to have requests routed to the correct (home) SDM and so an SLF isused.

According to present IMS standards, the SLF receives SDM queries andredirects the querying network element to the appropriate SDM. Forexample, 3GPP (23.228, 29.228 and 29.329) identifies an SLF whichoperates as a Cx and Sh re-direct routing service. As shown in FIG. 2 atstep 1, a network element AM 20 sends the intended Cx/Sh query to SLF22. The SLF uses an internal routing table to return a Diameter redirectreply providing the address of the appropriate SDM 24—in this exampleSDM B—to handle the Cx query (step 2). At step 3, the AM resends theCx/Sh query to SDM B. SDM B then returns the Cx response to the AM (step4). Note that the SLF is a distinct Diameter service requiring each AMto maintain separate SLF and SDM sessions. Typically, AMs make theirfirst query to the SLF then cache the returned SDM address for use insubsequent queries.

The SLF approach used in present IMS standards suffers from certaindrawbacks.

Network complexity can be a problem since the SLF must appear as adistinct service to the SDM and each network element must maintainseparate Diameter sessions to the SLF and the SDM

Handling a change of the home SDM for a subscriber (as a result of asite failure through disaster or a matter of administrativereorganization) can also be a problem. This requires that each networkelement that might interact with the SDM on behalf of the subscriber beupdated with new Diameter connection to the new SDM. This is asignificant processing overhead for each subscriber that is “moved” fromone SDM to another and for large subscriber moves a very high processingoverhead with impact on latency as well.

Also, using the re-direct routing service forces network elements to becapable of handling Diameter re-direct replies which adds complexity tothe network elements. Moreover, increased processing overhead isincurred at the network element as a result of redirection.

An object of the present invention is to provide an improved SLFapproach.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda method of handling queries for subscription data for a user of acommunications network, comprising the steps of: a Subscriber LocationFunction (SLF) receiving a query for subscription data for a user from anetwork element of an Internet Protocol Multimedia Subsystem (IMS)network, the query comprising an identity of the user; the SLF lookingup in a database the user identity to identify a subscriber data serverin which the user's subscription data can be found; and the SLF proxyingthe query to the identified subscriber data server.

Advantageously, by proxying the query to the subscriber data server (egHSS or SDM), the network element (eg CSCF, AS or AM) need not be capableof handling Diameter re-direct replies from the SLF and need not incurthe processing overheads involved. The network element need not be awareof any partitioning of the subscriber data service at all. Also, networkcomplexity is reduced since separate Diameter connections (andpotentially security associations) need not be maintained between allnetwork elements on the one hand and all subscriber data servers on theother hand. Thus, moving subscribers from one subscriber data server toanother is simpler and involve less processing overheads and reducedlatency. Thus network operator CAPEX and OPEX may be reduced.

In one embodiment, the method comprises the steps of: the SLF receivinga response to the query; and the SLF sending the response back to thenetwork element.

In one embodiment, the IMS network comprises a plurality of subscriberdata servers each holding a subset of the total subscriber data for thenetwork.

In one embodiment, the SLF is co-located with one of the subscriber dataservers. Advantageously, co-location provides a reduction in networkcomplexity by reducing the number of discrete elements. Also, since aseparate, discrete SLF requires a subset of the subscription datamaintained across all partitions (eg a mapping from user identity tosubscriber data server) it will require (geo) synchronization andredundancy mechanisms separate and in addition to those alreadyoperating in the subscriber data management service. Throughco-location, the (geo) synchronization and redundancy mechanismsrequired for the subscriber data service may be re-used for thesubscriber location functions. In another embodiment, the SLF is a standalone mechanism to the plurality of subscriber data servers.

In one embodiment, the subscriber data server is a Home SubscriberServer (HSS). In one embodiment, the network element is a Call SessionControl Function (CSCF). In one embodiment, the network element is anApplication Server (AS). In one embodiment, the query is a Cx query. Inone embodiment, the query is an Sh query.

Further aspects of the present invention are set out in the appendedclaims. Further advantages of the present invention will be apparentfrom the following description.

In order to show how the invention may be carried into effect,embodiments of the invention are now described below by way of exampleonly and with reference to the accompanying figures in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary implementation of a partitioned SDM (ie HSS)in a large communications network according to the prior art;

FIG. 2 shows the functioning of re-direct SLF according to the priorart;

FIG. 3 shows the placement options for a proxy SLF 30 for eachgeographic region according to the present invention;

FIG. 4 shows the functioning of proxy SLF 30 according to the presentinvention;

FIG. 5 shows the functioning of a proxy SLF co-located with its regionalSDM according to the present invention in contrast to the functioning ofa re-direct SLF where queries are for “local” subscribers;

FIG. 6 shows the functioning of a proxy SLF co-located with its regionalSDM according to the present invention in contrast to the functioning ofa re-direct SLF where queries are for “remote” subscribers; and

FIG. 7 shows the functioning of an SLF co-located with its regional SDMaccording to the present invention where subscription data has beenre-homed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are described below by way ofexample only. These examples represent the best ways of putting theinvention into practice that are currently known to the Applicantalthough they are not the only ways in which this could be achieved.

FIG. 3 shows the placement options for a proxy SLF 30 for eachgeographic region according to the present invention. There are fouroptions: 1) network level placement; 2) co-located with the SDM; 3)regional level placement and 4) co-located with each network element.

Placement needs to address two key issues. Network element query latencyand data management complexity associated with keeping SLF data in syncwith SDM data distribution.

The preferred option is to co-locate the SLF with the SDM (option 2) forthe following reasons. Co-locating the SLF with the SDM enables the SLFto use the same data management infrastructure, sharing data, robustnessand redundancy mechanisms used by other services at the SDM. Whereas, aseparate SLF element means that explicit data synchronization,replication and administration infrastructure/processes are required.Options 1, 3 and 4 compound this functional complexity by increasing thenumber of SLF's in the network that have to be kept in sync with SDMdata. The larger the number the harder it is to ensure all (SLFs andSDMs) are synchronized while avoiding time-based discrepancies. Elementco-location (option 4) is the extreme case requiring for example 20(regions)×4 (SDMs)×3 (element types)=240 relationships to manage over 60SLFs, excluding any inter-SLF relationships and additional elementsintroduced at a later date. Furthermore, the bulk of interactions willbe between the AM and SDM, and only the first query for a subscriberwill involve the SLF. In placing the SLF outside the SDM the trade offis reducing the latency of that initial query against increaseddistributed data management complexity imposed on the SDMs.

FIG. 4 shows the functioning of proxy SLF 30 according to the presentinvention. Note that this figure, and subsequent figures, shows a Cxinteraction between AM 20 and an SDM 24. The present invention appliesequally to Sh and other interfaces between a network element andsubscriber data server in an IMS network.

At step 1, AM 20 sends the Cx query to SLF 30. The query includes as aparameter the identity of the user for whom subscription data is beingqueried. The SLF looks up the user identity in its database to identifyan SDM (SDM B) at which subscription data for the user may be found andat step 2 proxies the Cx query to the identified SDM. At step 3, the SDMreturns the Cx response to the SLF which forwards the response to the AMat step 4. Optionally, the SDM adds its address as a new “tag” attributevalue pair (AVP) in the response message so that the AM can extract theAVP and cache the SDM address for subsequent queries. Alternatively, theAM can interpret the origin-host AVP and cache the SDM address forsubsequent queries without the SDM adding it's address as a new “tag”.This enables the AM to send subsequent subscription data queries to theappropriate SDM directly.

As a result, the proxy SLF presents itself to network elements such asthe AM as an SDM service, as opposed to the re-direct approach where theSLF presents itself as a separate service. Also, the network elementsneed not be aware that there is a partitioning of the SDM service.

FIG. 5 shows the functioning of proxy SLF 30 co-located with itsregional SDM 24 according to the present invention in contrast to thefunctioning of re-direct SLF 22 where queries are for “local”subscribers. Where the subscriber is in the local SDM, the first queryis more efficient in the proxy SLF approach of the present inventionsince the Cx query is not re-directed back to AM 20 but proxied by SLF30 to SDM 24—in this case SDM A. Since SDM A and SLF 30 are co-located,this is very efficient. Subsequent queries can be sent to correct SDMbased on a “tag” AVP in the Cx response message providing the address ofSDM A.

Network architecture is based on assumption that bulk of subscriberactivity will be in “home” region and therefore with “home” SDM, so theproxy approach is expected to be more efficient than the re-directapproach in this respect.

FIG. 6 shows the functioning of proxy SLF 30 co-located with itsregional SDM 24 according to the present invention in contrast to thefunctioning of re-direct SLF 22 where queries are for “remote”subscribers. Where the AM needs to establish a session to a subscriberin a “remote” SDM region, the first Cx query needs to be routed ineither case. According to the present invention, SLF 30 proxies the Cxquery to SDM B which returns a response to the AM via the SLF.Optionally, the SDM adds its address as a new “tag” attribute value pair(AVP) in the response message so that the AM can extract the AVP andcache the SDM address for subsequent queries. Alternatively, the AM caninterpret the origin-host AVP and cache the SDM address for subsequentqueries without the SDM adding its address as a new “tag”. It can beseen that both schemes are roughly equivalent in terms of efficiency.

FIG. 7 shows the functioning of an SLF co-located with its regional SDMaccording to the present invention where subscription data has beenre-homed. When a subscription record for a user is moved from SDM A toSDM B, proxy SLF 30 provides a means to dynamically inform a networkelement such as AM 20 of the new SDM address. When AM 20 send its Cxquery to proxy SLF 30 co-located with SDM A at step 1 (either becausethis is its first query or because it has received an error onattempting to direct a query to SDM A directly), SLF 30 proxies (step 2)the query to SLF 32 which forwards (step 3) the query to SDM B. Theresponse is then returned (steps 4-6) to AM 20 via SLFs 32 and 30.Alternatively, SLF 30 may proxy the response directly to SDM B andreceive a response directly.

1.-30. (canceled)
 31. A network element, comprising: a memory; and atleast one processor coupled to the memory, wherein the at least oneprocessor is configured to: send a query for subscription data for auser to a Subscriber Location Function (SLF), wherein the networkelement is in an Internet Protocol Multimedia Subsystem (IMS) network,wherein the query comprises an identity of the user, wherein the SLF isconfigured to proxy the query to a subscriber data server in which theuser's subscription data can be found and; and receive, from the SLF, aresponse to the query.
 32. The network element of claim 31, wherein theIMS network comprises a plurality of subscriber data servers eachholding a subset of the total subscriber data for the network.
 33. Thenetwork element of claim 31, wherein the subscriber data server is aHome Subscriber Server (HSS).
 34. The network element of claim 31,wherein the network element comprises a Call Session Control Function(CSCF).
 35. The network element of claim 31, wherein the network elementcomprises an Application Server (AS).
 36. A non-transitory computerreadable memory medium storing program instructions executable by aprocessor to: receive a query for subscription data for a user from anetwork element of an Internet Protocol Multimedia Subsystem (IMS)network, the query comprising an identity of the user; determine asubscriber data server in which the user's subscription data can befound; and proxy the query to the identified subscriber data server. 37.The non-transitory computer readable memory medium of claim 36, whereinthe program instructions are further executable by a processor to:receive a response to the query from the identified subscriber dataserver; and send the response to the network element.
 38. Thenon-transitory computer readable memory medium of claim 36, wherein theIMS network comprises a plurality of subscriber data servers eachholding a subset of the total subscriber data for the network.
 39. Thenon-transitory computer readable memory medium of claim 38, wherein oneof the subscriber data servers comprises the processor.
 40. Thenon-transitory computer readable memory medium of claim 38, wherein astand alone mechanism to the plurality of subscriber data serverscomprises the processor.
 41. The non-transitory computer readable memorymedium of claim 36, wherein the query is a Cx query.
 42. Thenon-transitory computer readable memory medium of claim 36, wherein thequery is an Sh query.
 43. A method, comprising: by a subscriber locationfunction (SLF): receiving a query for subscription data for a user froma network element of an Internet Protocol Multimedia Subsystem (IMS)network, the query comprising an identity of the user; determining asubscriber data server in which the user's subscription data can befound based on the identity of the user; and proxying the query to theidentified subscriber data server.
 44. The method of claim 43, furthercomprising: receiving a response to the query from the identifiedsubscriber data server; and sending the response to the network element.45. The method of claim 43, wherein the IMS network comprises aplurality of subscriber data servers each holding a subset of the totalsubscriber data for the network.
 46. The method of claim 45, wherein theSLF is co-located with one of the subscriber data servers.
 47. Themethod of claim 45, wherein the SLF is a stand alone mechanism to theplurality of subscriber data servers.
 48. The method of claim 43,wherein the subscriber data server is a Home Subscriber Server (HSS).49. The method of claim 43, wherein the network element is a CallSession Control Function (CSCF).
 50. The method of claim 43, wherein thenetwork element is an Application Server (AS).